1. It would give the other 12 teams in the AL a better chance at actually making the playoffs.
2. It would mean that, in a three-round playoff (DS, CS, WS) ONE of those two teams would not make the playoffs every year.
3. It would give Fox, ESPN and any other national broadcaster of MLB ratings GOLD by guaranteeing three times the number of Yankees-Red Sox games every year.
4. It would give MLB justification to go to four divisions in the NL as well.
Yes, I've already thought that one out, too:
NL South: Atlanta, Florida, Washington, Houston
NL North: Colorado, Chicago, Milwaukee, Saint Louis
NL East: New York, Philadelphia, Pittsburgh, Cincinnati
NL West: Los Angeles, San Diego, San Francisco, Arizona